The present invention relates to manhole covers and more particularly to covers having a system for moving the cover to and from a closing position over the manhole.
Manholes comprise three basic elements, namely, a ring serving as a top lip of the manhole, a skirt connected to and below the ring to form a partially enclosed chamber or hole, and a cover to cooperate with the ring for removably covering the chamber.
The size and weight of manhole covers have increased throughout the last several decades. Today, 36, 42, and 48 inch diameter or cross length are common with thickness of 1/2 and 3/8 (stiffened) inches. Covers are usually made of diamond plate steel and can weigh as much as 100 pounds.
Many techniques for raising and moving manhole covers have been tried to aid the operator. Bars, levers, frames, and hoists have all been tried but with essentially no acceptance in the field primarily because of the bulk and size of these aids that require movement and storage at the station or on the service truck.
Therefore, large covers today are still manually raised and dragged to the side, causing risk of injury to the operator. Also, because many covers have precisely positioned features, the operator must replace the cover in a precise angular position over the manhole, which is quite difficult with an unaided cover.